In recent years, for the purposes of effective use of oil resources and emission reduction of CO2, fuel consumption reduction of vehicles, such as automobiles, etc., is eagerly required. For that reason, a demand of fuel consumption reduction for a lubricating oil composition that is used for engines of vehicles, such as automobiles, etc., is also becoming strong.
For example, PTL 1 discloses a lubricating oil composition for internal combustion engine, in which an ashless dispersant, a polymethacrylate-based viscosity index improver whose PSSI (permanent shear stability index) falls within a predetermined range, and the like are contained in a lubricating base oil, and a ratio of a viscosity index and an HTHS viscosity (high temperature high shear viscosity) at 100° C. is regulated to a predetermined range.
PTL 1 mentions that the foregoing lubricating oil composition for internal combustion engine is high in torque reduction rate under conditions of an oil temperature of 80° C. and good in fuel consumption reducing properties in a high-temperature region as compared with the conventional ones.